Here is what I have learned to do in similar situations:
1. Ask to see the evidence, such as an EKG, if appropriate, and ask the doctor to show you where the murmur is.
2. Ask yourself what symptoms you are suffering as a result of the supposed problem -- nausea, pain, dizziness, weakness, loss of appetite, inability to exercise daily, or what?
3. Consider getting a second opinion.
4. Be sure to ask your doctor to rate the problem: On a scale of 1 to 10, with 10 being the worst recorded, where is your supposed problem?
5. Ask yourself if your doctor thinks there is an actual problem, and if so where the threat is -- or is your doctor simply being precautionary. (I personally do not support the precautionary principle as a guide.)
6. If an actual problem has been identified, ask about the range of treatments if any. (I try to start with the mildest treatment and work up, but many doctors like to start in the middle and back up if the treatment injuries the patient. Your choice.)
Sometimes Wikipedia is helpful as the first step in research. It is always best to test it by checking other sources you consider reliable.
http://en.wikipedia.org/wiki/Heart_murmur